There have been many threats against various facilities and human rights promulgated by terrorists or other groups intent on destroying property and killing people in order to impart panic and terror in today's society. Many of these threats and attempts at disruption employ man made devices, which devices can be placed in a small vehicle or hidden in conventional places. Such threat enabling devices may be activated by means of remote control or various other mechanisms, and explode at will. It is often difficult to detect or otherwise discriminate such man made devices from their environment by conventional means. The detection and location of these man made devices is of great importance in mitigating many kinds of threats.
Small threats are typically very difficult to detect since they are of low radar cross-section, may be slow moving, or perhaps static, and may be situated in an environment of clutter interference. For example, of importance is the detection of electronic hardware or circuits associated with small classes of weapons and unmanned vehicles. This is especially true in the detection of small UAV systems. In such circumstances, conventional radars that depend upon primary (or direct mirror-like) radio reflections of their transmitted wave forms are relatively non-effective detectors of man made devices and of such threats. In a conventional radar system, increasing the illuminating signal power and correspondingly the energy returned from such objects within a radar beam to achieve improved transmission/range or improved detection sensitivity does not fundamentally improve an object's signal to clutter signal ratio and thus it's detectability under clutter dominated conditions (note that in this instance both the signal power of the object and it's background clutter power will be raised by the same degree and that this does not increase the object's signal to background clutter power ratio that is fundamental for increased detectability). Increased radar receiver gain yields the same, no net detection value result under clutter dominated conditions. Thus, by providing greater transmitted radar illumination power and/or greater receiver gain, one does not change the object's signal to clutter signal ratio. Moreover, Doppler discrimination is of limited value in the discrimination of slow moving or static objects of interest within a background of clutter having similar behavior. It is understood that if one has a non-moving object then Doppler radar is ineffective in detecting the object.
In combination with the above-noted problems the additional challenge of detecting weak signals from relatively small objects within a large background of interfering signal energy is extremely difficult utilizing conventional radar systems. Secondary radars or transponders are typically employed to detect and track the above-noted types in like environments. However, these objects must be technically cooperative or friendly in the sense of operating active transponding electronics designed for such applications. Thus, as one can ascertain, one can track a small vehicle by conventional radars if the vehicle contains a suitable transponder, and therefore is capable of returning a signal which can be detected as distinct from background signals. However, non-cooperative targets would not use such transponders. For example, a terrorist utilizing a small vehicle or having a man made destructive device on the vehicle would not incorporate or use such transponders.
In order to solve the above-noted problems a parametric radar system utilizes radio energy analogous to that associated with conventional radars. However, the system is designed to ignore or otherwise not receive or process primary or directly reflected energy from objects.